Descaling of titanium and alloys thereof



United States Patent 3,502,503 DESCALING 0F TITANIUM AND ALLOYS THEREOF Louis J. Bartlo, Youngstown, and Octavian Bertea and Layne F. Plock, Warren, Ohio, assignors to Reactive Metals, Inc., a corporation of Delaware No Drawing. Filed May 10, 1967, Ser. No. 637,339

Int. Cl. C23g 1 28 US. Cl. 134-2 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to descaling titanium. More particularly, the invention concerns a novel method of descaling titanium.

Oxide coatings and scale form on titanium and titanium alloys when heated to elevated temperatures. Scales that form on titanium surfaces at temperatures up to 1000 F. are generally thin and can be removed by acid pickling. However, heating titanium or its alloys for long periods of time or to high temperatures results in a formation of thick, adherent oxide scales that cannot be removed simply by acid pickling. Such scales must either be removed by mechanical means or by a chemical treatment designed to loosen the scale in normal acid baths or both.

Several commercial descaling baths are presently available for removal of scale on titanium alloys. However, all of the present commercial processes have characteristics that limit their usefulness as descaling media for a wide range of titanium products.

The titanium industry produces numerous products in a variety of thermal conditions. Presently available descaling processes do not have sufficient versatility to handle all of these products. For example, a number of age hardenable alpha-beta alloys are being produced in the solution-treated condition. These alloys require scale removal at temperatures below 600 F. to avoid altering metallurgical structure or properties. On the other hand, certain alpha alloys are fabricated at extremely high temperatures and have scales that are generally diflicult to remove. Such alloys require high descaling temperatures for eflicient scale removal. There is, therefore, a great need for a descaling media that can be operated efiiciently over a broad temperature range.

A number of present commercial descaling baths are limited to operating temperatures above 800 F. because of their high melting points. One process referred to as the sodium hydride process has this disadvantage since it too is limited to fairly high operating temperatures, i.e. 650 to 750 F. An additional disadvantage of this bath is that it utilizes a reducing media and causes undesirable hydrogen contamination in most titanium alloys.

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Low temperature aqueous descaling baths, such as disclosed in US. Patent No. 3,121,026, which require 10 to 20% water to maintain a liquidity, can be used for descaling. However, such baths have been found to be ineflicient since they require excessive descaling time and repeated acid pickling to accomplish satisfactory scale removal. Moreover, these baths typically have relatively low maximum operating temperatures rendering them unsuitable for 'broad spectrum applications. The operating temperature limit of aqueous baths is usually about 475 to 500 F. which is too low for descaling many titanium materials.

The present invention provides a method of descaling titanium and titanium alloys which is operable over a wide temperature range, i.e. 450 to 1000 F., and which can therefore accommodate a Wide variety of titanium products and which avoids the problem of hydrogen contamination as well. The invention involves an improvement in the process for treating titanium or titanium alloy articles having undesirable scale on the surface thereof for the purpose of removing same which comprises contacting said article with a substantially non-aqueous liquid bath consisting essentially of a mixture of 35 to 50% by weight potassium nitrate and 50 to by weight potassium hydroxide at a temperature in the range of 450 to 1000 F., rinsing to remove the mixture and then treating with acid. The final acid treatment removes the last vestiges of scale and residue but the KOHKNO accomplishes primary scale removal. Several rinsing and acid pickling cycles may be performed if desired. In contrast to prior available descaling baths, the present invention provides a method of descaling various titanium products over a considerable temperature range and can, therefore, accommodate different products at different optimum conditions. Thus, for example, age-hardenable titanium alloys may be advantageously treated at temperatures between 500 and 600 F. and non-age-hardenable materials can be most effectively treated at temperatures of 750 to 800 F.

The following examples will illustrate the practice of the invention and its elfectiveness under different conditions for treating a variety of titanium products. A series of samples were prepared in 1 by 2-foot panels of production material with typical mill scale. The scale producing conditions are described in Table I. The panel sections were treated in the preferred bath composition containing 55% KOH and 45% KNO at various temperatures for varying times and the results are shown in Table II. The variety of materials treated successfully show the great versatility of the present invention. The production sheet materials were descaled in a 2 by 2 by 4-foot gas-operated steel tank which contained approximately 550 pounds of KOH and 450 pounds of KNO The descaling operation was carried out by immersing the sheets in the bath for the prescribed temperature and time. The sheets were then water rinsed and dipped in 10% HO to insure removal of remaining residue and caustic. Following the sulfuric acid dip, the sheets were again water rinsed and immersed in 3 to 4% HF-25-30-% HNO acid bath for final cleanup.

TABLE I removed from each of the alloys. The optimum descaling Unanoyed Ti FHR Finish bottomed conditions for various alloys are summarized in Table D FHR+EA Finish hot rolled, electric furnace annleal: 1,350 F., 30 min., air TABLE In 000 Ti-4Al-3Mo-1V ST Solution treat: 1,625 F., 7 min., Approximate Descaling Time in water quench. Mlnutes at- T1-5Al-2.5Sn FHR Finish hot rolled. Tl-6Al-4V ST Solution treat; 1, 5o 10., m, All y Condltlon 1 550 F. 700 F. 800 F.

water quench. T1-5A1-4V CR+EA Cold rolled, electric furnace gg T1 +EA g Zfi 1,475 F-mm-air 'ri-lxl-ii ivjjjjiljl S 5 11- 535553 1 THAI-4V FHR+EA Finish hot rolled electric furnace 0 gtgifi 3. 5 5 nneal: l,475 1 1 hr., furnace Ti GA1 4v CR EA "53 9001130 13000 's air c001 T1 6A1 4V FH R+EA 10 15 540 Tl-BAl-lMo-IV EA Ellesctric furnace ainneal: 1,450" E, TMAHMEE} EA 5 5 m1n., alr coo Ti-13V-l1Cr-3Al CR+EA Cold rolled electric furnace anneal: CR+EA cycles 10 H0 1,450 F.,15 min., air cool. Tl'sMn FHR+EA 5 5 Tl-8Mn FHR+EA Finish hot rolled, electric furnace 15 1 See Table I for sealing conditions.

anneal: 1,250" F.2 1hr., furnace 2A cycle consists of Ill-ruin. descale, water quench, 5-min., 10% cool to 900 F., air cool. H1804, water rinse and dry. Last cycle is followed by 5-min. pickle ln 3% HIP-% HNOK.

3 Number of cycles is dependent on scale condition.

In addition to the excellent descaling characteristics of 20 the bath, hydrogen pick up was found to be unusually low on all the titanium grades investigated. These results are illustrated in Table IV which reports the hydrogen data obtained prior to and following descaling.

TABLE IV Hydrogen Aiter Descaling and Pickling 2 Base Hydrogen 500 F., 550 F., 600 F., 700 F., 800 in, Condition Avg. Range 40 min. 40 min. 20 min. 10min. 5mm.

R a 115 106-129 109 89 106 123 114 FHR+EA 4 65 -79 79 so 69 ST 4 112 -126 115 114 F113 9 71 59-92 65 74 63 66 73 sT 6 92 54-124 94 61 95 CR+EA 44 40-50 40 47 44 50 44 FHR-l-EA 4 63 37-102 57 63 47 74 57 Ti-8A1-1Mo-1V 76 52-115 69 79 72 70 72 Ti-l3V-11Cl'-3Al CR-l-EA 9 116 114-123 118 116 117 Ti-sMii FHR-l-EA 4 103 84-124 92 /106 105 110 117 1 See Table I for scaling conditions. 2 Single analysis unless otherwise noted; 3 Average of 11 analyses. 4 Average of 12 analyses. 6 Average of 10 analyses; Average of 9 analyses. TABLE H We have found that although the time articles are in gf gg T Bath Perscerllt the bath is not critical for achieving good quality surfaces, Alloy Condition min: g g i a preferred treating period of up to about 40 minutes is TF6 A1 4V CR+EA 20 550 100 beneficial, however, the treating tune is governed prim T l-6Al-4V sT 20 550 100 45 11y by the tenacity of the scale being removed and the ggigi- :8 $38 igg operating temperature of the bath. Low operating temper- :ST 10 700 100 tures usually require the longest descaling time while 3+ g ggg 8? treatment times of 3 to 5 minutes are common at operat- EA 20 550 100 ing temperatures of 700 to 850 F., where the nature g; g 538 g3 50 of the titanium material permits the use of these temper- EA 20 550 100 atures. g2 338 13% An interesting observation in connection with the de- EA 20 550 100 scaling of titanium alloys and products thereof is that 52 g 388 :88 the aqueous baths of the same materials, i.e. potassium ST 20 550 75 55 hydroxide and potassium nitrate do not operate as effg $83 3% fectively in descaling as the molten salt baths in ac- Ti-13v-11oi-3AlI s1 5 700 9g cordance with the invention. Moreover, it has been fur- Unalloyed EA g 333 igg ther observed that the sodium hydroxide and sodium nitrate respectively are not effective substitutes for potas- Panels of Ti-6Al-4V, Ti-5Al- 2.5Sn, Ti-8Al-1M0-1V, 60 sium hydroxide and potassium nitrate. This is demon- T1-8Mn, T1-13V-1lCr-3Al and T1-4Al-3Mo-1V were destrated by the percent scale removal obtained in a series scaled at 550 F. for 20 minutes and rinse-pickled in of tests on panels of dififerent alloys treated in the de- 3-4% HF-2530% HNO All materials descaled very scaling media at recommended temperatures. The results well with the exception of the Ti-4Al-3Mo-1V and Tiof these tests are described in Table V, which show that 13V-11Cr-3A1 which showed some scale remaining. Pan- 65 although certain alloys descale well in all baths, the deels of unalloyed T1, T1-6Al-4V, Ti-5Al-2.5Sn, Ti-8A1- scaling of some alloys was improved only when treated in 1 Mo-IV, T1-8Mn and T1-13V-11Cr-3A1 were dcscaled at accordance with the invention with a mixture of potas- 700 F. for 5 and 10 minutes. The scale was completely slum nitrate and potassium hydroxide.

TABLE V Bath Composition Temp" Percent Descaled in 20 minutes wt. percent F. Ti-13V-11Cr-3Al Ti-4A1-3Mo-1V Ti-6Al-4V Ti-16V-2.5Al Ti-BMn 20 min 75K0H-15KNO5-10H2O 20 min... 55KOH-35KNOa-1OH2O 20 min 55NaOH-45KNO5 55KOH-45KNOa 20 min 55Na0H-45NaNO The unpredictability of the effectiveness of descaling media is illustrated in Table V above. However, in addition to the above, further evidence of the impossibility of satisfactorily predicting descaling effectiveness was obtained by tests conducted on a large number of experimental baths investigated in various combinations, Among the materials tested in descaling media for titanium and titanium alloys were the following:

NaCl K2S207 Na CO CuCl NaF SrCl Na B 07 Na SO CI'203 KBr CaCl KHSO The baths containing the above materials in various com binations were screened in a similar manner to the tests described above but using smaller, i.e. 1-inch by 2-inch test coupons of several titanium sheet grades. The results indicated that potassium salts are superior to sodium salts but that only the mixtures of potassium hydroxide and potassium nitrate in the ranges specified, i.e. 50 to 65% KOH, 35 to 50% KNO were efiective over the required temperature range for a sufiiciently wide variety of titanium products.

We claim:

1. An improvement in a process of descaling articles of a metal from the group consisting of titanium and titanium alloys which avoids undesirable hydrogen contamination which comprises contacting said articles with a substantially non-aqueous mixture consisting of about 45% by weight potassium nitrate and about 55% by weight potassium hydroxide at a temperature inthe range of 450 to 1000" F. to remove scale from the surfaces thereof, rinsing and pickling in acid for residue removal.

An improvement according to claim 1 comprising treating articles of age-hardenable titanium alloy by contacting same with said mixture of potassium nitrate and potassium hydroxide at a temperature in the range of 500 to 600 F.

3. An improvement according to claim 1 comprising treating articles of non-age-hardenable titanium alloy by contacting same with said mixture of potassium nitrate and potassium hydroxide at a temperature in the range of 700 to 850 F.

4. An improvement according to claim 1 wherein said articles are in contact with said mixture of potassium nitrate and potassium hydroxide for up to about minutes.

5. An improvement according to claim 1 wherein said titanium article is given more than one acid pickling treatment following contact with said potassium nitrate and potassium hydroxide mixture.

6. An improvement according to claim 5 wherein said titanium article is given a first acid pickling in dilute sulfuric acid, rinsed and then given a second acid pickling in a mixture of nitric and hydrofluoric acids.

References Cited UNITED STATES PATENTS 2,458,660 1/1949 Webster 1343 XR 2,458,661 1/1949 Webster et al 13427 XR 2,674,550 4/1954 Dunlevy et al. 1343 2,826,539 3/1958 Murtland 134-29 XR 3,010,854 11/1961 Satterfield 13427 3,121,026 2/1964 Beigay 134-2 MORRIS O. WOLK, Primary Examiner I. T. ZATARGA, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 502 503 March 24 1970 Louis J Bartlo et a1 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Table V, first column, line 4 thereof, SSNaOH- ISNaNO" should read SSNaOH-4SNaNO Signed and sealed this 29th day of December 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

